Origins of life

Rolfe

Adult human female
Rolfe
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We used to be told that the spontaneous arising of all the complexities of life was an extraordinarily improbable event, but the reason it happened was the enormous wodges of time available for it to happen. If you have enough monkeys typing for long enough you'll eventually get the complete works of Shakespeare.

Mmmmm.

But then it turns out that life seems to have arisen almost as soon as conditions on the planet were right for it to arise.

OK.

Now we have speculation about life on other planets, starting with Mars but also looking at planets in other solar systems. And it seems to be taken as read that if conditions are right for "life as we know it, Jim" to arise, then it will arise.

Now it's one thing to postulate that just that once the monkeys will get the complete works of Shakespeare, and the reason we're here to speculate about it is that here is where it happened to happen. However it seems to me to be something else again to assume that every time you get a few monkeys together, they're soon working busily on Hamlet.

Then I hear explanations about a natural tendency towards complexity, which balances the natural tendency to disorder. Seems to be found in certain types of clay. So maybe it isn't monkeys and Shakespeare at all, but a natural tendency of the system to evolve life when the right inorganic conditions are met. I don't know much about this theory, but it does sound a lot more satisfactory as an explanation than the typing monkeys.

Anybody know anything about this?

Now, if we take "life as we know it Jim" to be not only carbon-based, but based on the same biochemistry of nucleic acids and proteins and lipids and so on, what is the likelihood of a system evolving independently being similar to the one we're familiar with? I mean the same molecules doing the same jobs at the cellular level. Is this a question which can be answered in any sensible way? I'm particularly interested in the likelihood of the genetic code being the same. Does anyone know if the coding of each individual triplet for a particular amino acid is logical, based on anything about the shapes of the molecules, or is it just an arbitrary relationship?

It's the idea of answering these sorts of question that really excites me as far as the prospect of finding life on some other planet is concerned. How closely is our biochemistry pre-specified by the inherent properties of the inorganic system, and how much is just happenstance? If we found organisms with the same triplets coding for the same amino acids, would that prove that these organisms had a common origin with life on Earth, or might this really be an inevitability of the system through which life arises when conditions are right?

I'd just like to hear what other people think about this one. And yes, it isn't a coincidence that I posted this when Ian was banned - it's too close to his "infinitesimally improbable events happening repeatedly" dead end for me to want him getting loose on it.

Rolfe.
 
Yeah, I thought that might be the case. Still, if anyone wants to speculate wildly, be my guest!

I'd be interested to know if anyone has established whether there is a shape relationship between a base triplet and the amino acid it codes for, or if it's believed to be random. I can't remember ever coming across anything about this.

Rolfe.
 
Originally posted by Rolfe

Anybody know anything about this?
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Not really, no. Pretty much guesswork at this point.
I'd be interested to know if anyone has established whether there is a shape relationship between a base triplet and the amino acid it codes for, or if it's believed to be random. I can't remember ever coming across anything about this.
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Not a direct shape relationship, but it's not random either. It is determined by the dihydrouridine loop of the tRNA molecule being acted upon by the enzyme aminoacyl-tRNA synthetase. (Well, you asked).
 
Just wildly speculating here, but I think that amino acid formation is about as random as two atoms of oxygen and one atom of hydrogen makes a water molecule. That is to say that life is just as natural "what ever that means". I know this doesn't make any sense because I have this idea in my head that I can't articulate it yet. Maybe one day.
 
Rolfe said:

Then I hear explanations about a natural tendency towards complexity, which balances the natural tendency to disorder. Seems to be found in certain types of clay. So maybe it isn't monkeys and Shakespeare at all, but a natural tendency of the system to evolve life when the right inorganic conditions are met. I don't know much about this theory, but it does sound a lot more satisfactory as an explanation than the typing monkeys.
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I remember a little from my semester of 'Astronomy and life in the universe'. Basically before life, you have an abundance of clays. Because due to weather conditions clays dry out, periodically get soaked, etc new clays form all the time. (BTW clays have somewhat a crystal structure, and a flake of one type of clay landing in a drying pool can start crystalisation of itself) So say you have 2 types of clay to start with. One flakes easily when it dries, and the other does not. When they both dry, the first one flakes and wind may carry the flakes very far. If they land on the right type of clay they can transfer their pattern to it. Thus clay A is a more sucessfull replicator than clay B.

Also I think it has been observed that some clays generate certain chemicals to stop themselves drying out entirely (and thus damaging themselves).


Rolfe said:

Anybody know anything about this?

Now, if we take "life as we know it Jim" to be not only carbon-based, but based on the same biochemistry of nucleic acids and proteins and lipids and so on, what is the likelihood of a system evolving independently being similar to the one we're familiar with? I mean the same molecules doing the same jobs at the cellular level. Is this a question which can be answered in any sensible way? I'm particularly interested in the likelihood of the genetic code being the same. Does anyone know if the coding of each individual triplet for a particular amino acid is logical, based on anything about the shapes of the molecules, or is it just an arbitrary relationship?
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Don't know. Even if I did I wouldn't tell you. (I'd quickly go tell the nobel prize panel) :)

I think the these are the main questions about life formation. Interestingly all the amino acids we have are one 'handed', and they can't bond to opposite handed molecules. (i.e. not their mirror images). There are a couple of theories about how this could have occured, because most natural processes make a mixture of left and right handed molecules. One method that was suggested to me was polarized starlight. This seems pretty unlikely to me, but then again I have no idea how much light in space is polarized in a particular direction.
 
I don't view abiogenesis as a product of random chance. It is a product of specific chemistry. If you have the right initial conditions, I think life would be an inevitable result. The work of abiogenesis it to determine exactly what those initial conditions are and where on Earth they would have existed around 4
billion years ago (no small task given that we don't even have any rocks existing that are that old). I do however suspect that the conditions for life to arise (at least as we know it) are quite specific and may not be at all common in the universe.
 
Originally posted by Rolfe

Does anyone know if the coding of each individual triplet for a particular amino acid is logical, based on anything about the shapes of the molecules, or is it just an arbitrary relationship?
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The synthetases which are primarily responsible for matching the proper amino acid to a tRNA molecule are themselves products of the same system of decoding. It is not inconcievable that a system evolving along a different line might have resulted in synthetases which performed the matching differently, producing entirely different proteins from the same nucleotide sequences (or the same proteins from different sequences). I think what you are really asking is whether the available design space contains alternative synthetases capable of performing the matching. This is a bit like asking whether a particular Turing machine will terminate; the answer will not be yes or no, it will be yes or unknown.
 
According to Star Trek, pretty nearly every bipedal species can interbreed with humans, so their genomes must be awfully similar.

I'vre read items in Science (either original reports or citations of work published in Nature or elsewhere) referring to the role clay minerals may have played. Their small size and electronic activity (related to their ion-exchange capabilities), as well as their ubiquitousness, could make them effective in mediating biogeochemical reactions.

I've seen an additional item arguing that having formed, certain chiral molecules can catalyze the formation of additional molecules of the same handedness.

And one more item discussing the synthesis of an amino acid or protein (or some such biologically-important molecule) or two that does not normally occur in nature--perhaps these could form naturally under somewhat different conditions than prevailed on ancient Earth.
 
Great thread, Rolfe!

I've also wondered if there are different chemicals that would set up similar to Amino Acids, given different temperatures/environments. For instance, what sets up in clay on Venus? Some sort of metallic analogue? And how about the moons of Saturn, or Saturn or Jupiter themselves?

The different energies and compounds available in thes environments....could it engender different lifeforms with completely different chemical makup?
 
Badger said:
Great thread, Rolfe!

I've also wondered if there are different chemicals that would set up similar to Amino Acids, given different temperatures/environments. For instance, what sets up in clay on Venus? Some sort of metallic analogue? And how about the moons of Saturn, or Saturn or Jupiter themselves?

The different energies and compounds available in thes environments....could it engender different lifeforms with completely different chemical makup?
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If you stop using carbon it makes things a lot more difficult. On the other hand there are ways of producing most enzyme funtions without using amino acids.
 
I'm comfortable assuming that similar environments must yield similar life forms (chemistry = biochemistry = biology = true everywhere in the universe).

The only interesting factoid is that we are the only species we know that can pick up a rock and throw it. Also, we do not run from fire, rather we use it. Factor in electrical skills and general science, and we become unique and invincible.

Further factor in race, and I think it's fair to ask why Africa seems to exist in static tribes, affected only by their own genocidal behavior once they are GIVEN western prosperity, while Asian and English civilizations seek advancement as their very cultural identity. I ain't racist, but I'm not going to pretend not to judge one society as more human than another when the lesser behaves like animals.
 
Rolfe said:
...Then I hear explanations about a natural tendency towards complexity, which balances the natural tendency to disorder. Seems to be found in certain types of clay. So maybe it isn't monkeys and Shakespeare at all, but a natural tendency of the system to evolve life when the right inorganic conditions are met. I don't know much about this theory, but it does sound a lot more satisfactory as an explanation than the typing monkeys.

Anybody know anything about this?...
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Er, no, not formally, but as it happens I've just got round to reading "Deep Simplicity" by John Gribbin. He talks about life being one natural result of a complex system involving the interactions in a network between living and non-living components. One relatively simply example is the transfer of sulphur (on Earth), apparently necessary for life, between the oceans and the land and the way in which life is integral to the chemical processes involved. His story suggests that without life, all the sulphur would be washed into the ocean and trapped there in some sulphur compound.

He also seems to suggest, more fundamentally, that the complex chemical precursors for life are attractor states in the phase space of the complex chemical network. I'm talking beyond my wit here so I'll just say that the book is very compelling to someone without any real basis in chemistry, physics, maths or biology, neither does it appear to lean on philosophy as a means of explanation. Not sure how people here would view Gribbin, is he recommended?
 
geni said:
If you stop using carbon it makes things a lot more difficult. On the other hand there are ways of producing most enzyme funtions without using amino acids.
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How does it make things a lot more difficult? Is it the energy required to maintain an analogous system based on, say silicone? Or does it have more to do with the structure itself?
 
It's the structure. The four-square bond system of carbon is almost uniquely suited to form long, complex, "organic" molecules. Sorry, Horta, but it's unlikely that silicon could be the basis of the sort of molecules needed for life that's even close to "as we know it".

That was why I was confining the speculation to a system basically the same as the one we're familiar with, and wondering how much leeway there was at the biochemical level for variations on the theme.
Not a direct shape relationship, but it's not random either. It is determined by the dihydrouridine loop of the tRNA molecule being acted upon by the enzyme aminoacyl-tRNA synthetase. (Well, you asked).
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Thatks, Dynamic, I see what you're getting at. That's a very interesting observation.

Rolfe.
 
@Rolfe, just on a point of clarification, Si forms exactly the same structures of bonds as does C, except that Si-Si multiple bonds (i.e. unsaturated systems) are far less common. C-C bonds are however much more likely on the basis that their bond strength are almost twice as great as Si-Si bonds; hence the propensity of C to "catenate" to give long chain, complex molecules. The biological ubiquity of carbon is therefore on energetic grounds rather than structural.

As an aside I have read somewhere arguments on the biological ubiquity of water, which held that water was the ideal solvent in which biology (i.e. life) was to occur. An alternative solvent such as ammonia is a possibility.

PS I read your recent contribution to the "debate" on the homeopathy forum. You are truly a doctor and I know I'd take my mog to you if you were practising.
 
I just wish I was better at chemistry when I was in college. Then maybe I could contribute something intelligible to this.

As for American's remark, each society does what makes one successful. Asians moved onto an area where advancement was essential to survival, they had to evolve or die. In Africa you find it was a bountiful area, and they obviously have/had large populations. They are being tested in their survival now. It is a do or die situation. Judging from most clinging to "old ways" (female excision, useless health care practices) we are finding the population succumbing to disease ( a large percent in some areas have AIDS) and starvation (when bad farming practices lead to dust bowl situations).
Gavin Hart at the National Aids Trust in the UK said the South African Government had been slow to react to the Aids crisis and still refused to accept the link between HIV and Aids.
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http://news.bbc.co.uk/1/hi/health/719183.stm


The health minister then went on to recommend that those infected with HIV eat garlic, lemons and olive oil. “Garlic is absolutely critical, we need to do research on it. We cannot just ridicule it.”
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Yep, "natural" is better than "drugs". http://www.wsws.org/articles/2004/feb2004/stha-f16.shtml

They will eventually have to educate themselves, but the old ways will have to die out first, taking some of the population with it. I'm sure the Asians suffered greatly at some points in the areas of Japan and such. Then look at the former USSR and China though. Their reasonings and communism have me scratching my head. Look at Germany and rise and fall of another fascist state.

Humans are diverse, and what won't work will cause failure. Thankfully we live where we do, and we seem to be working things out in what seems to be a more common sense manner. Then we get crazy governments who figure god will just hand us what we need instead of allowing for us discovering it for ourselves.

Heck, the Jehovas figure god will just hand us another paradise planet to live on once we no longer die and our planet is overpopulated (after the "rapture" all the good people on the planet get brought back alive and nobody dies ever again).

So if we stop speculating, as Rolfe is encouraging us do to here, and we stop searching for answers, we will die out when this planet does, or sooner. Our only saviour will be technology and science, since they allow us to figure things out and solve problems ourselves.

It's funny. We should accuse the sCAM folks and no-mind health ministers like the one in South Africa of population control. They are allowing, and telling people to die of disease (directing them to use garlic instead of "western medicine") when it can be prevented. What will be left are the people educated enough to understand that. Therefore, only scientists will survive, and the ultra religious, plus homeopath and naturopath supporters who reject vaccines and anti-virals will all die out.

Ha ha!
 
anor277 said:
@Rolfe, just on a point of clarification, Si forms exactly the same structures of bonds as does C, except that Si-Si multiple bonds (i.e. unsaturated systems) are far less common. C-C bonds are however much more likely on the basis that their bond strength are almost twice as great as Si-Si bonds; hence the propensity of C to "catenate" to give long chain, complex molecules. The biological ubiquity of carbon is therefore on energetic grounds rather than structural.

As an aside I have read somewhere arguments on the biological ubiquity of water, which held that water was the ideal solvent in which biology (i.e. life) was to occur. An alternative solvent such as ammonia is a possibility.

PS I read your recent contribution to the "debate" on the homeopathy forum. You are truly a doctor and I know I'd take my mog to you if you were practising.
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Oh, thanks, I knew there was some explanation. Energetic rather than structural. Yes, I remember being told that once. And water being the universal solvent and a lot of other really handy stuff about ice floating rather than sinking as any other material would do on solidifying.

Just take your mog to one of my clients....

No, I don't think we have any near you. Würzburg? I know I'm getting reasonably near to Bayreuth when I pass there. (Wagner nut, I'm afraid.)

Rolfe.
 
Thanks, anor277! I appreciate it.

This is probably off topic, but I was over at the Bad Astronomers board, and came across this http://anzwers.org/free/universe/ in one of the threads.

Based on 30 billion trillion stars, the above touched on chemistry info, and random chance, IMHO there's no friggen way that our little blue planet is the only one with life on it.

The fun part, as Rolfe has stated, is "What TYPE of life could there be?".

Sorry for the little derail.
 
Is there any life in matter or atom? Can there be dead matter & live matter? If live matter means with active energy? We are probanly discussing " Origins of life".:)
 
I heard some guy on the radio talking about the 'collectives of self catalyzing chemicals' and that they were probably important in abiogenesis.

He did say that getting to dna/rna was very diffuclt.

But I figure that in a universe as old as ours appears to be, the random chanes are very high.
 
Is there any life in matter or atom? Can there be dead matter & live matter? If live matter means with active energy? We are probably discussing " Origins of life".
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Consider water. We wouldn't call a glass of water alive. If you drink it, it becomes temporarily part of the chemical systems that make up your body. Later it leaves your body as sweat or urine or tears. The water didn't come to life in your body or die when it left your body. Water in your body is no different from water outside your body. The difference is only the chemical processes in which it is involved. Life can best be understood as a self sustaining, self replicating chemical process. It is more than the sum of it's parts. It has to be, since it's parts are constantly being replaced. You've probably replaced every water molecule in your body many times over the course of your life. You've certainly shed every inch of your skin numerous times. Your current body probably contains almost non of the original matter it contained when you were born.

Atoms themselves are lifeless. But atoms combined and reacting with each other in certain ways can produce more interesting things such as life.
 
espritch said:
Consider water. We wouldn't call a glass of water alive. If you drink it, it becomes temporarily part of the chemical systems that make up your body. Later it leaves your body as sweat or urine or tears. The water didn't come to life in your body or die when it left your body. Water in your body is no different from water outside your body. The difference is only the chemical processes in which it is involved. Life can best be understood as a self sustaining, self replicating chemical process. It is more than the sum of it's parts. It has to be, since it's parts are constantly being replaced. You've probably replaced every water molecule in your body many times over the course of your life. You've certainly shed every inch of your skin numerous times. Your current body probably contains almost non of the original matter it contained when you were born.

Atoms themselves are lifeless. But atoms combined and reacting with each other in certain ways can produce more interesting things such as life.
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espritch, Many thanks for one such best explaination. But if we still look deeply we may think that any substance which is active has life. Is it not so? Are matter or atoms become active or dead( something like ions & bounded) & if can, whether it can be said as origin of life?
 
Kumar. To have 'life' you have to be self replicating and utilize materials to do. You have to have DNA.

Water is not alive. Chemical reactions aren't life.

Self replicating simply means to be able to make more of yourself, but water only adheres or binds. H2O Does not make more H20. Oxygen cannot make more oxygen by reproducing. Exchange is not replication either.

A cell can become two by utilizing materials to make another of itself. Water cannot do this. Water can be used by the cell to do this, along with other materials.
 
But that may not represent origin. I think you meant biological life or vitalism. However origion of life must had started from the Energy>>Matter+ Energy levels

Few definitions of life:

1 a : the quality that distinguishes a vital and functional being from a dead body b : a principle or force that is considered to underlie the distinctive quality of animate beings -- compare VITALISM 1 c : an organismic state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction
2 a : the sequence of physical and mental experiences that make up the existence of an individual.

However, we may clarify it & discuss ' Origins of biological or human life'. It would have started by molecular formations of atoms into cells & then by mutations & differanciations in them.
 
Vitalism was debunked years ago. Life boils down to chemistry.
 
geni said:
Vitalism was debunked years ago. Life boils down to chemistry.
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But chemistry start with matter, energy, atoms, molecules>>>>etc.
 
anor277 said:
@Rolfe, just on a point of clarification, Si forms exactly the same structures of bonds as does C, except that Si-Si multiple bonds (i.e. unsaturated systems) are far less common. C-C bonds are however much more likely on the basis that their bond strength are almost twice as great as Si-Si bonds; hence the propensity of C to "catenate" to give long chain, complex molecules. The biological ubiquity of carbon is therefore on energetic grounds rather than structural.

As an aside I have read somewhere arguments on the biological ubiquity of water, which held that water was the ideal solvent in which biology (i.e. life) was to occur. An alternative solvent such as ammonia is a possibility.

PS I read your recent contribution to the "debate" on the homeopathy forum. You are truly a doctor and I know I'd take my mog to you if you were practising.
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The explanation I have heard is that the length of the bonds between carbon-carbon and carbon-hydrogen is just the right length so that an oxygen molecule cannot attack the carbon because the hydrogens cover the surface of the molecule. With Si the bonds are somewhat longer and so oxygen can attack and oxidize more easily. That explains why hydrocarbons are stable in a long tempertature interval while allowing complex molecules. Whether or not its possible to construct life using silicon as base if you also breathe chlorine gas or something instead of oxygen I have no idea.
 
American said:
...
Further factor in race, and I think it's fair to ask why Africa seems to exist in static tribes, affected only by their own genocidal behavior once they are GIVEN western prosperity, while Asian and English civilizations seek advancement as their very cultural identity. I ain't racist, but I'm not going to pretend not to judge one society as more human than another when the lesser behaves like animals.
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A fairer question would be ask what is so special with christianty that allowed science to progress and making the western world as powerful as it is today. If the africans had showed up in europe and killed, robbed and shipped off a large part of the population as slaves during the last 300 years or so I think the situation would have been the opposite.
 
The explanation I have heard is that the length of the bonds between carbon-carbon and carbon-hydrogen is just the right length so that an oxygen molecule cannot attack the carbon because the hydrogens cover the surface of the molecule. With Si the bonds are somewhat longer and so oxygen can attack and oxidize more easily. That explains why hydrocarbons are stable in a long tempertature interval while allowing complex molecules. Whether or not its possible to construct life using silicon as base if you also breathe chlorine gas or something instead of oxygen I have no idea.
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@Vitnir,
While the tendency of C to oxidize is undoubtedly important, energetics (i.e. thermodynamics) again dominates. A C-O bond is strong but not markedly so compared to a C-C bond. This is in contradistinction to say Si, for which a Si-O is markedly stronger than the homo-element Si-Si bond. Hence C can form long chains that are resistant towards oxidation (i.e. because there is no energy gain in C-C bonds forming C-O ones). Likewise C can form bonds with H, N, S, P etc. that are thermodynamically stable enough to perform complex chemistry and maybe (eventually) biogenesis.
 
Vitnir said:
The explanation I have heard is that the length of the bonds between carbon-carbon and carbon-hydrogen is just the right length so that an oxygen molecule cannot attack the carbon because the hydrogens cover the surface of the molecule. With Si the bonds are somewhat longer and so oxygen can attack and oxidize more easily. That explains why hydrocarbons are stable in a long tempertature interval while allowing complex molecules. Whether or not its possible to construct life using silicon as base if you also breathe chlorine gas or something instead of oxygen I have no idea.
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Bit technical for me. Is there something relevant to me in this posting??
 
anor277 said:
@Vitnir,
While the tendency of C to oxidize is undoubtedly important, energetics (i.e. thermodynamics) again dominates. A C-O bond is strong but not markedly so compared to a C-C bond. This is in contradistinction to say Si, for which a Si-O is markedly stronger than the homo-element Si-Si bond. Hence C can form long chains that are resistant towards oxidation (i.e. because there is no energy gain in C-C bonds forming C-O ones). Likewise C can form bonds with H, N, S, P etc. that are thermodynamically stable enough to perform complex chemistry and maybe (eventually) biogenesis.
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I'm not sure I follow your reasoning and its ten years since that teacher explained it to me though I think I remember the essence. It makes sense to me though to think it in 3D and imagine that the hydrogens cover the carbon so the oxygen cant "see" it. Oxidation usually starts at double bonds and other places where there are lacking protection from covering hydrogens. If the Si is slightly larger than a C you also need something bigger than H to form a protective surface against attackers. I dont quite understand how thermodynamics works in your example. Hydrocarbons give off a large excess energy as heat if burned and the only thing that keeps us from spontaneous combustion is this threshold that the hydrogens are responsible for.
 
@Vitnir, I’ll try to make things a bit clearer,

Bond strengths, C-C, 85 kcal mol-1, C-O 80 kcal mol-1
Si-Si. 55 kcal mol-1, Si-O 88 kcal mol-1

Therefore for a long C-C-C chain there is no thermodynamic driving force to promote oxidation. On the other hand, there is a potent thermodynamic force for Si-Si oxidation (88 - 55 = +33 kcal mol-1) for every Si-Si bond oxidized. Given that oxygen is abundant in the universe, Si-Si bonds are probably not the best choice for complex molecule formation.

Of course the fact that C binds to H (the most abundant substance in the universe) is equally important but not perhaps in the sense you mean. C-H (bond strength 105 kcal mol-1) are almost as energetic as O-H bonds (118 kcal mol-1), which is the other oxidation product. Compare this to Si-H bonds (77 kcal mol-1), oxidation of Si-H is thus much more thermodynamically favourable and therefore Si chemistry is a far less likely building block for biological molecules.
 
Rolfe said:
We used to be told that the spontaneous arising of all the complexities of life was an extraordinarily improbable event, but the reason it happened was the enormous wodges of time available for it to happen. If you have enough monkeys typing for long enough you'll eventually get the complete works of Shakespeare.

Mmmmm.

But then it turns out that life seems to have arisen almost as soon as conditions on the planet were right for it to arise.

OK.

Now we have speculation about life on other planets, starting with Mars but also looking at planets in other solar systems. And it seems to be taken as read that if conditions are right for "life as we know it, Jim" to arise, then it will arise.

Now it's one thing to postulate that just that once the monkeys will get the complete works of Shakespeare, and the reason we're here to speculate about it is that here is where it happened to happen. However it seems to me to be something else again to assume that every time you get a few monkeys together, they're soon working busily on Hamlet.
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With the obligatory caveats about sample size and all that, there is one rather critical piece of data now available. Specifically, the fact that "life seems to have arisen almost as soon as conditions on the planet were right" suggests either that we were really freakishly lucky, or that it's not as improbable as previously believed.

The monkeys may not be busy working on Hamlet; they may just be trying to find the 'g' key. We don't know. But what we would expect to find if life really were that unbelievably impossible is

a) we'd be alive (since we need to exist to find it, pthththt to you Ian), and
b) there would be a long gap between the achieving of the conditions and the actual appearance of life.

Since that's not what we find, it's at least a valid working assumption that the appearance of life is "normal," which implies a mechanism, which in turn provides a goal for search. Depending upon what mechanism one finds, there are a lot of possibilities for how many different structures would fit that mechanism (and how widely dispersed "the right conditions" are).
 
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